docs: def export(datastore_key, calc_id=-1, exports='csv', export_dir='.'):
      """
      Export an output from the datastore.
      """    
      dstore = util.read(calc_id)
      parent_id = dstore['oqparam'].hazard_calculation_id
      if parent_id:
          dstore.parent = util.read(parent_id)
      dstore.export_dir = export_dir
      with performance.Monitor('export', measuremem=True) as mon:
          for fmt in exports.split(','):
              fnames = export_((datastore_key, fmt), dstore)
              nbytes = sum(os.path.getsize(f) for f in fnames)
              print('Exported %s in %s' % (general.humansize(nbytes), fnames))
      if mon.duration > 1:
          print(mon)
      dstore.close()